The present invention relates to a pen printer for drawing desired figures and signs such as characters or numeric values with a detachable pen on paper.
In a conventional pen printer of the type described above, a pen is detachably held in a pen holder and the pen holder is driven in different directions to draw desired figures and signs such as characters or numeric values with the pen. In this case, the pen held by the pen holder is moved with the home position as a reference point. Pen printers include compact ones (e.g., CADLINER, available from MAX Inc.) for drawing parts numbers and names in drawings and large-sized ones for drawing large drawings. The principle of operation of these pen printers is the same as that of X-Y plotters. Pens used in the above pen printers are replaced with other pens to change colors and line thicknesses of figures to be drawn on paper. In the conventional pen printers, however, only special pens (whose pen body portions held by the pen holder have the same diameter) are used, and commercially available general pens (body portions held by the pen holder have different diameters) such as ball-point pens and felt pens (generally called sign or marking pens) cannot be used. A conventional pen holder consists of a pen support member for receiving one side of the pen body and a pen press member for pressing the other side of the pen body. The tip of the pen held in the pen holder is located at a position separated from the pen support member toward the pen body by half of the distance between the pen support member and the pen body (if the pen tip is aligned with the central axis of the pen body). Even if various types of special pens having the same diameter and the same pen tip position are selectively held in the pen holder, the pen tip position is always the same. However, when a pen having a diameter different from that of the special pen is held in the pen holder, the pen tip position is different from that of the special pen. The positions of figures and signs drawn by general-purpose pens deviate from those drawn by the special pens. In particular, when a special pen is replaced with a general-purpose pen during drawing of figures or signs, the sign positions on each line are not aligned and deviations in lines in the figure become distinct.
In a conventional X-Y plotter having the same principle of operation as that of the pen printer, a pen is moved along X- and Y-axes to draw figures and signs (including characters and numeric values). The conventional X-Y plotter includes a carrier frame driven along guide rails and moved along the Y-axis and a pen support member supported by the carrier frame and driven along a direction (i.e., the X-axis) perpendicular to the moving direction of the carrier frame. The pen support member is moved along the X-axis by a pen support drive mechanism (e.g., a belt drive mechanism) arranged in the carrier frame. In the conventional X-Y plotter, a Y drive mechanism for moving the carrier frame along the Y-axis is arranged independently of an X drive mechanism for moving the pen support member along the X-axis. In a conventional compact plotter for drawing only small signs such as characters and numeric values, the X and Y drive mechanisms must be accommodated in a small space, resulting in a complicated structure.
A self-driven pen printer is known as another conventional pen printer which runs along the paper surface to draw a desired figure.
The self-driven pen printer is also called a pen robot and a typical example thereof is "TURTLE", (tradename) available from TERAPIN Inc. This pen printer includes a running member, a pen holder and a pen holder operation mechanism. The running member has two drive wheels and two free-running wheels and runs along the paper surface. The pen holder is located at an intermediate position between the two drive wheels. The pen holder operation mechanism causes the pen holder carried on the running member to move vertically, thereby bringing the pen in contact with the paper surface or separating it therefrom. The running member can be driven in any direction by controlling the rotational speed and direction of the two drive wheels. The pen held in the pen holder is brought in contact with the paper surface upon downward movement of the pen holder and draws a figure or sign corresponding to the moving pattern of the running member. For example, if the running member runs linearly, a straight line can be drawn on the paper surface. If the running member is turned, an arc can be drawn on the paper surface.
When one of the two drive wheels is stopped while the other continues to be driven so that the running member is turned with the minimum radius of rotation, the radius of the drawn arc (the arc whose center is the stopped drive wheel) is 1/2 of the distance between the two drive wheels, because the pen holder is located at the intermediate position between the two drive wheels. The conventional self-driven pen printer cannot draw an arc having a radius smaller than 1/2 of the distance between the two drive wheels.
In the conventional self-driven pen printer, since the pen holder is located at the intermediate position between the two drive wheels, the line drawn on the paper surface with the pen cannot be visually checked until the printer passes the drawn line. It is thus impossible to draw a desired figure by visually controlling the printer running direction. In other words, only figures of predetermined patterns preset in a printer controller can be drawn in the conventional self-driven pen printer.